Center for Medical Genomics, Pennsylvania State University, University Park, USA.
Mol Biol Evol. 2010 Nov;27(11):2446-50. doi: 10.1093/molbev/msq143. Epub 2010 Jun 9.
To achieve dosage balance of X-linked genes between mammalian males and females, one female X chromosome becomes inactivated. However, approximately 15% of genes on this inactivated chromosome escape X chromosome inactivation (XCI). Here, using a chromosome-wide analysis of primate X-linked orthologs, we test a hypothesis that such genes evolve under a unique selective pressure. We find that escape genes are subject to stronger purifying selection than inactivated genes and that positive selection does not significantly affect the evolution of these genes. The strength of selection does not differ between escape genes with similar versus different expression levels in males versus females. Intriguingly, escape genes possessing Y homologs evolve under the strongest purifying selection. We also found evidence of stronger conservation in gene expression levels in escape than inactivated genes. We hypothesize that divergence in function and expression between X and Y gametologs is driving such strong purifying selection for escape genes.
为了实现哺乳动物雌雄个体之间 X 连锁基因的剂量平衡，一条女性 X 染色体失活。然而，失活染色体上约有 15%的基因逃避 X 染色体失活（XCI）。在这里，我们使用灵长类动物 X 连锁同源基因的全染色体分析来检验一个假设，即这些基因在独特的选择压力下进化。我们发现，逃避基因受到的净化选择比失活基因更强，而正选择对这些基因的进化没有显著影响。在男性和女性中表达水平相似和不同的逃避基因之间，选择的强度没有差异。有趣的是，具有 Y 同源物的逃避基因在进化过程中受到最强的净化选择。我们还发现，逃避基因在表达水平上比失活基因具有更强的保守性。我们假设 X 和 Y 配子体之间功能和表达的差异是导致逃避基因如此强烈的净化选择的原因。
